repl-watcher

Send a command to the REPL on file changes inside a component.

Usage

Include it in your system, and give it the paths to watch, and a command to run

(:require [repl-watcher.core :refer [repl-watcher])

This example watches source files, and runs reloaded.repl/reset when changes are detected.

(component/system-map
;; ...
:auto-reset (repl-watcher ["src/clj" "src/cljs"] "(reloaded.repl/reset)")
;; ...

When any files along the paths are changed, (reloaded.repl/reset) gets sent to the currently running repl.

Rationale

I wanted to watch for source changes directly in my component, without spinning up a separate repl.

When evaluating how to run a (reloaded.repl/reset) programmatically, I was running into issues with resets.

The issues stem from tools.namespace.repl, which provide ways of hot-reloading. However, doing so programmatically leads to very strange issues, if not reset from a running repl. They work differently, which is a bit of a surprise. The issue comes down to this error:

IllegalStateException("Can't change/establish root binding of: *ns* with set")

See this blog for details:

http://justabloginthepark.com/2017/06/18/clojure-and-the-esoteric-mysteries-of-namespaces/

TODO

Currently finds the repl to connect to by .nrepl-port in the project root. May be other connection schemes in the future.

Implementation details

Currently Hawk sometimes is a little loud when it comes to file watching, if a file is modified multiple times, eg in a VM. This library comes with a 2 second window where it ignores events, which is sufficient for my use cases.

License